Casting equipment for use in the fabrication of rotor secondary windings



July 19, 1966 A. L. REDIGER ETAL CASTING EQUIPMENT FOR USE IN THEFABRICATION OF ROTOR SECONDARY WINDINGS Original Filed May 14, 1962 2Sheets-Sheet 1 A/V/kL. Z 498; Ju//Z1$ 5/01 er;

y 19, 1956 A. L. REDIGER ETAL 3,

CASTING EQUIPMENT FOR USE IN THE FABRICATION OF ROTOR SECONDARY WINDINGSOriginal Filed May 14, 1962 2 Sheets-Sheet 2 United States Patent 4Claims. (ill. 22-150) This is a division of our co-pending applicationSerial Number 194,540, filed May 14, 1962. This invention generallyrelates to the manufacture of dynamoelectric machine rotors having castsquirrel-cage secondary windings and more particularly to castingequipment suitable for use in fabricating such rotor windings. In themass production of laminated rotors incorporatmg cast squirrel-cagewindings, that is, conductor bars integrally joined at each end of alaminated stack by end rings, there has been a practical difficulty inproviding accurately skewed conductor slots while maintaining economy inthe fabrication of the rotors; i.e., relatively low equipment andprocess costs. In one approach, punched out laminations, formed withvent holes or ducts betwen the rotor bore and the slots, are initiallystacked such that a number of spiraling pins enter the vent holes toskew the slots. The stacked laminations are then compressed by elaborateequipment and while held under compression, the squirrel-cage winding iscast on the stack by a pressure or centrifugal casting technique. Notonly is this procedure costly due to the type of equipment and laborinvolved, but in addition Where no vent holes exist in the laminations,it is impossible to follow this procedure to obtain an accurate skew ofthe slots.

With specific reference to the manufacture of rotors having counterboresand balance weights attached on studs made integral with end rings tocompensate for an unbalance in the mass system with which the rotor isassociated; e.g., a single piston compressor with a crankshaftintroducing a dynamoic unbalance into the system, difiiculty has alsobeen experienced in satisfactorily securing the laminations together,especially in the region of the counterbore where the bore of thelaminations is in spaced relation to the stationary rotor supportingstructure. Furthermore, when the balance weight mounting studs areintegrally provided with one end ring, there is a tendency for the studsand winding to be cast with a non-uniform density as a result of (atleast in part) voids contained in the hardened casting, which in turnadversely affect the conductivity of the winding and the dynamic balanceof the rotor, both conditions being detrimental to the performance ofthe rotor.

Accordingly, it is a primary object of the present invention to provideimproved yet inexpensive casting equipment and it is a more specificobject to provide such equipment which obviates at least some of theundesirable features mentioned above in regard to cast squirrel-cagewindings for use in dynamoelectric machine rotors.

It is a further specific object of the invention to provide improved dieequipment, capable of providing cast windings of dynamoelectric machinerotors, which not only eliminates the need for removing casting spruesbut also minimizes cold flow of the casting material and other causes ofcasting voids while insuring generally uniform density throughout thefinished cast winding.

In carrying out the objects of the present invention in one form, weprovide equipment for use in the fabrication of a cast secondarysquirrel-cage winding formed by angularly spaced apart conductorscarried in axially aligned slots of a rotor core which are joinedtogether at each end by short-circuiting end rings. A die plate adaptedto be placed at each end of the core has an annular end ring cavitycorresponding to the desired configuration of the end ring. One of theplates has a plurality of angularly spaced apart and tapered sprue portsfurnished with inserts. Each insert has, in turn, an egress projectinginto the end ring cavity for the introduction of casting materialtherein, such as aluminum. Where balance weight studs integrally joinedto the end ring are esired, additional cavities may be provided incommunication with the end ring cavity for this purpose. The number ofports preferably approximate the number of slots in the rotor core, withthe cross-section area of each insert being substantially in the rangeof 00069-00145 square inch, and with the ratio of the cast material tothe total cross section egress area being below seven. With thisconstruction, in spite of the low cost equipment utilized, spruesresulting from the casting operation will be recessed beneath the outersurface of the end ring and will not interfere with the mounting ofbalance weights on the studs next to the end ring, if such are employed,thereby eliminating any need for their removal by a subsequent machiningoperation. Further, cold flow of the casting material and other causesof casting voids and non-uniformity in material density are minimized.At the same time, should it become desirable after long service, theinserts may readily be removed and replacements substituted for them.

The subject matter which we regard as our invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. Our invention, itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof may best be understood by reference 'to the followingdescription taken in connection with the accompanying drawings whichillustrate the preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a fragmentary top view of loosely arranged stamped out rotorlaminations in stacked relation;

FIGURE 2 is a side elevational view, partly broken away, illustratingthe application of a weld on the periphery of the laminations of FIGURE1 when the conductor slots are disposed in skewed axial register and thestack is held under compression;

FIGURE 3 is a partial side elevational View, broken away in parts, ofthe welded stack of laminations in position preparatory to the castingoperation for forming the stack with a cast squirrel-cage windingemploying the preferred embodiment of our invention;

FIGURE 4 is a view similar to that of FIGURE 3 illustrating the castingoperation;

FIGURE 5 is an enlarged fragmentary view in section of a portion of thedie and sprue port structure of the equipment shown in FIGURES 3 and 4;

FIGURE 6 is a fragmentary sectional view through the rotor, illustratingthe step of finishing the periphery of the rotor into a smooth accuratedimension while simultaneously removing at least a portion of the welds;

FIGURE 7 is a view in perspective, partially broken away to illustratestructural details, of th finished rotor fabricated in accordance withthe preferred embodiment of the invention; and

FIGURE 8 is an enlarged fragmentary side view in section of a part ofthe rotor of FIGURE 7 to show details. I

Referring now to the drawings in more detail, for purposes ofexplanation, the preferred embodiment of the invention has been appliedto the manufacture of an induction rotor 19 (FIGURE 7), suitable for usein a motorcompressor unit to drive a single piston compressor (notshown) in which the compressor crankshaft introduces a dynamic unbalanceinto the mass system with which the rotor is associated. An example ofthis type of unit is illustrated in the US. Patent No. 3,157,805, of W.R.

Hoffmeyer and J. H. Johnson, granted on November 17, 1964, and assignedto the same assignee as the present application.

In the present exemplification, FIGURES 1-6 inclusive disclos the rotorof the exemplification being fabricated. More specifically, as shown inFIGURES 1 and 2, we initially assemble a predetermined number of discshaped laminations 11 and 12, conventionally stamped out of magnetizablesheet iron or steel material. To illustrate the invention, laminations11 and 12 include central holes 13 and 14 respectively, and a pluralityof angularly spaced apart closed conductor slots 15 disposed radiallybeyond the central holes and adjacent periphery 16 of laminations, whichis somewhat rough from the tearing action in the punch operation. Inorder to achieve a skew of the conductor slots and the proper alignmentof the central holes, the laminations may be loosely arranged in a stack17 on a suitable fixture (see FIGURE 2), in which a base 21 is providedwith three angularly spaced apart (e.g., approximately 120) upright rodsor pins 22 for receiving slots 15 and spiralling them at the properangle to form skewed conductor passageways extending entirely throughthe stack. Central holes 13 are aligned to furnish a bore adapted tohave an interference fit with a rotatable shaft (not seen) and enlargedholes 14 of laminations 12 provide a counterbore for accommodating apart of the stationary rotor supporting structure of themotor-compressor unit (not shown) in spaced relation.

After the laminations have been arranged on the fixture as previouslydescribed, they are then compressed axially with approximately the sameforce as that required for the subsequent casting operation. Generallyspeaking, the necessary mini-mum force is in the neighborhood of 100pounds per square inch of gross punching area. While stack 17 is held inaxial compression, several welds are applied in a predetermined fashion(to be explained hereinafter) on peripheral surface 16 to secure thelaminations firmly together in the desired relation for subsequentfabrication steps. FIGURE 2 shows one inexpensive yet satisfactorymanner in which the foregoing may be readily accomplished. The equipmentincludes a rotatable turntable 24 on which base 21 is fixedly attachedand a revolvable piston assembly 25, having apertures 26 to comple--ment the ends of skewing rods 22, and capable of regulated compressivemovements toward and away from turntable 24.

It should be noted at this time that We prefer to fuse the skewed orspiraled stack of laminations together by at least two, preferably threebut not substantially more, light or shallow Welding beads 27, providedin generally equally spaced apart angular relation on the peripheralsurface 16 of stack 17. These beads should extend the longitudinallength of the stack on the solid portion thereof, intermediate andparallel to a pair of adjacent conductor passageways defined by slots15. Preferably the depth of weld penetration into the stack is shallowin extent; that is, the penetration should be such that during theturning down step in which the peripheral surface of the stack isfinished into an accurately dimensioned cylindrical surface (FIGURE 6),a greater portion, if not all, of the welding bead itself may be readilyremoved. As an example, for

a nominal three inch diameter stack, the penetration should not besubstantially in excess of inch beyond the finished peripheral surfaceof the stack. In this way, the possibility of introducing undesirableand uncontrolled dynamic unbalance and rotor noise are essentiallyprevented.

In actual practice, satisfactory results hav been obtained with the useof a commercially available are welding machine employing inerttungsten, with the welding head 28 suitably mounted to move parallel tothe skew of the laminations. The welding machine, one of straightpolarity, had the following characteristics: welding current-l50 toamps; welding voltage10 volts; weld speed-40 to 50 inches/minute;electrode diameter inch; and pure argon shielding gas flowing between 15to 20 cubic feet per hour. For indexing turntable 24 to lock the stackin the proper location relative to welding head 28, a common plungerassembly 29 may be utilized. Once the welding operation has beencompleted, piston 25 is raised and the stack of laminations removed fromfixture 20.

The welded together stack may be annealed in the conventional way forstress relieving purposes and either stored for subsequent use orconveniently transported by conveyor (not shown) to the castingoperation. It will be appreciated that, among other things to beexplained hereinafter, welds 27 function as a temporary holding fixturefor maintaining the stack of laminations under compression both prior toand during the casting process, now to be described in connection with apressure type aluminum casting procedure shown in FIGURES 3 and 4.

Turning now to the illustrated pressure type casting apparatus orequipment employed in the casting operation, it comprises a castingchamber 30 and a pressure ram head 31 positioned directly above thechamber and capable of being reciprocated relative to the chamber by anysuitable means, as by a hydraulic driving piston. Chamber 30 is formedin halves which are hinged at 34 upon a trunnion shaft 35 mounted in asuitable base 36. The two halves are normally held together by adetachable connection or latch 37. A heated pot 32 containing a supplyof molten casting material 33, e.g., aluminum, is located on base 36next to chamber 31 for conveniently transmitting the correct amount ofmolten material by 'a ladle or the like to chamber 30 at the start ofeach casting cycle.

In the preferred embodiment of our invention the casting dies forforming the squirrel-cage winding include an upper die plate 40 (asviewed in the drawings), adapted to be removably positioned at one sideface of stack 17, and a lower die plate 41 for mounting at the otherside of the stack, adjacent the counterbore of the rotor in theexemplifioation. The plates are maintained in tight engaging relation atthe stack side faces for the casting process by a rod 42 fastened at oneend to the center of lower plate 41 and extending up through the bore ofthe stack. The other end of the rod passes through plate 40 and islocked thereto by the threaded interengagement between externallythreaded rod end 43 of the upper end of rod and a nut 44 partiallyreceived in plate depression 45. Through the threaded engagement of aninterially threaded hole 46 formed in ram head 31 and the externallythreaded rod end 43, the laminated stack and the attached die plates maymove as a unit with the ram head.

With reference to the preferred casting die form-s, plates 40 and 41respectively include generally annular end ring forming cavities 52 and51 conforming in cross section to the desired ring configuration. Eachcavity has a somewhat U-shaped molding wall in communication with theends of the skewed conductor passageways defined by slots 15 foradmission of molten metal, denoted by number 53 in FIGURE 3. Lower dieplate 41 is provided with a pair of spaced apart elongated slightlytapering downwardly extending weight supporting stud cavities 54 and 55.As shown in FIGURE 3, the casting entrances of the stud cavities arecontained on the bottom wall (as viewed in the drawing) of cavity 51. Aplurality of spruing ports 57 for the introduction preferably of metal53 from chamber 30 to the cavity 51, preferably frusto-conical inconfiguration and corresponding in number to the number of conductorpassageways incorporated in the rotor, vare disposed around the bottomwall of cavity 51, several of the ports being included between studcavities 54 and 55. An insert or sleeve 58 is positioned in each portsuch that its egress 59 pIOJCCtS a short predetermined distance intocavity 51. The taper of the ports and inserts is in the neighborhood of5", with the insert egress having the minimum cross section area forlocking and fluid guiding purposes.

For best casting results, the egress cross-section area for theindividual inserts should be substantially in the range 0.0069 to 0.0145square inch, and the ratio of the Weight of the casting material inpounds relative to the total egress area in inches should be belowseven. As will become more apparent hereinafter, the casting.arrangement just described eliminates the necessity of machining ofl?sprues normally formed during the casting process while permitting theeasy and inexpensive replacement of parts, such as inserts 58, afterlong continued use. Further, during the casting operation the foregoingminimizes the possibility of cold flow of the casting material and otherundesirable causes of voids, to assure a filling of the cavities and aWinding and supporting studs of enhanced uniform density.

Referring now in particular to the casting procedure, operation isinitiated with the component parts in the position shown in FIGURE 3,that is, with the assembled die, stack, and ram head unit raised abovechamber 39 which has the requisite amount of molten aluminum. Head 31 islowered at a speed of 6575 feet per second until lower die plate 41enters the confines of chamber 30. Continued downward movement of theplate 41 causes the molten aluminum to be forced upwardly with apreselected pressure through inserts 58, first into cavities 51, 54 and55, then through the slot passageways into upper cavity 52, filling allcasting spaces in the stack and plates. Trapped gases in the dies may beexhausted to the atmosphere through Vents in die 40 which aresufficiently small to prevent the escape of molten metal from thecasting cavities.

Since stack 17 and the die plate are at a lower temperature than themolten aluminum, they absorb heat from the aluminum, hardening it. Itwill be observed from FIG- URE 4 that the hardened aluminum in the diesand stack 17 provide conductor bars 61 in the slot passageways,integrally joined at each end by annular end rings 62 and 63, to formthe squirrel-cage winding, as Well as studs 64 and 65 for supportingbalance weights 66 (FIGURE 7). In addition, as seen in FIGURES 4 and 5,with the egresses 59 of the frusto-conical shaped port inserts 58extending upwardly into bottom cavity 51, a conical sprue 67 is producedwithin egress 59 which mates in a point contact with hardened upstandingrunners 68 of an excess metal slug 69. Upon upward movement of ram head31 once again to the raised position of FIGURE 3, sprues 67 and runners68 shear at a point beneath the outer surface 70 (FIGURE 5).Consequently, egresses 59 furnish tapered recesses 71 in end ring 63surrounding sprues 67 which do not have to be removed by a subsequentmachining step. Hardened slug 69 may thereafter be returned to heatedpot 32 to be liquefied for re-use.

Upon completion of the casting procedure, die plates 40, 41 and stack 17are dismantled from ram head 31 and the laminated stack is disassembledfrom between the plates. Thereafter stack 17 is transferred to the finalturning operation, illustrated by FIGURE 6, where the outer periphery ofthe stack is turned down to an accurate diameter by any suitable means,such as cutting tool 73, to produce an accurately dimensioned smoothfinished rotor surface 16a. Coincident with this surface finishing step,a major portion, but not necessarily all, of each weld 27 is removed.Either before this finishing step is performed or after it has beenaccomplished, balance weights 66 (one being shown in FIGURES 7 and 8)can be secured in place on studs 64 and 65 by a simple stakingprocedure.

The completed rotor 10, formed in accordance with the preferredembodiment of our invention, is shown in FIG- URES 7 and 8, revealingcertain advantageous features of the invention, especially significantwhen the rotor is of the type having balance weights and a counterboreat one end for accommodating a part of the rotor supporting structure.An improved cast winding and studs of enhanced uniform density areprovided, and in spite of the fact that casting sprues 67 have not beenremoved by a machining operation, balance weights may be attached inclose proximity to outer surface 70 of the end ring 63 withoutinterference in the mounting by the sprues. Moreover, should it becomedesirable after long service, certain component parts of the castingequipment, such as casting inserts 58, may easily be removed andreplaced with new ones.

It should be apparent to those skilled in the art, while we have shownand described what at present is considered to be the preferredembodiment of our invention in accordance with the patent statutes,changes may be made in the structure disclosed without actuallydeparting from the true spirit and scope of this invention, and wetherefore intend to cover in the following claims all such equivalentvariations as fall within the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. For use in the manufacture of a rotor including cast conductorscarried by aligned slots in the rotor and interconnected at each end toform a squirrel-cage winding, a die for casting the winding comprising aplate including a generally annular cavity to be arranged at one end ofthe core and in communication with the slots, said plate including aplurality of angularly spaced apart sprue ports each having an egressprojecting into said cavity for the introduction of casting material,the cross-section area of each egress being substantially in the range0.0069- 0.0l45 square inch.

2. For use in the manufacture of a rotor including cast conductorscarried by aligned slots in the rotor and interconnected at each end toform a squirrel-cage winding, a die comprising a plate including agenerally annular cavity arranged at one end of the core and incommunication with the slots, said plate including a plurality ofangularly spaced apart tapered sprue ports each having an insert withits egress projecting into said cavity for the introduction of castingmaterial, the number of ports approximating the number of aligned slotsin the rotor, the cross-section area of each insert being substantiallyin the range 0.0069-0.0145 square inch, and the ratio of the castmaterial to the total cross section egress area being below seven.

3. For use in the manufacture of a rotor including cast conductorscarried by aligned slots in the rotor and interconnected at each end toform a squirrel-cage winding, a die comprising a plate including agenerally annular cavity arranged at one end of the core and incommunication with the slots, said plate including at least two spacedapart studs forming cavities opening into said annular cavity and aplurality of angularly spaced apart frusto-conical shaped sprue portseach having an insert with its egress projecting into said cavity forthe introduction of casting material, the number of ports approximatingthe number of aligned slots of the rotor, with at least one portdisposed between said stud forming cavities, the cross-section area ofeach insert being substantially in the range 0.0069- 0.0145 square inch,and the ratio of the total weight of the cast material to the totalcross section egress area being below seven.

4. For use in the manufacture of a rotor including cast conductorscarried by aligned slots in the rotor and interconnected at each end toform a squirrel-cage winding, die means for casting the windingcomprising an assembly including a first cavity of preselectedconfiguration ar ranged at one end of the core and in communication withthe slots; said assembly including at least second and third cavitiesopening into said first cavity, and a plurality of spaced apart sprueports each having an insert with its egress projecting into said firstcavity for the introduction of casting material, with at least one portdisposed between said second and third cavities, with the cross-sectionarea of each insert being substantially in the range 0.0069- 0.0145square inch, and with the ratio of the total weight of the cast materialto the total .cross section egress area being below seven.

References Cited by the Examiner UNITED STATES PATENTS 2,065,213 12/1936Del-an et al 22-68 2,807,844 10/1957 Hemphill.

J. SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Examiner.

1. FOR USE IN THE MANUFACTURE OF A ROTOR INCLUDING CAST CONDUCTORSCARRIED BY ALIGNED SLOTS IN THE ROTOR AND INTERCONNECTED AT EACH END TOFORM A SQUIREEL-CAGE WINDING, A DIE FOR CASTING THE WINDING COMPRISING APLATE INCLUDING A GENERALLY ANNULAR CAVITY TO BE ARRANGED AT ONE END OFTHE CORE AND IN COMMUNICATION WITH THE SLOTS, SAID PLATE INCLUDING APLURALITY OF ANGULARLY SPACED APART SPRUE PORTS